Method for producing metal cylinder, method for producing substrate for electrophotographic photoreceptor, method for manufacturing electrophotographic photoreceptor, and metal slug for impact pressing

ABSTRACT

A method for producing a metal cylinder includes preparing a metal slug having a surface adjusted so that the crystal grain diameter at a depth of 10 μm from the surface is smaller than that at a depth of 100 μm from the surface, and the crystal grain diameter at a depth of 10 μm from the surface is 30 μm or more and 120 μm or less; and forming a cylinder by impact pressing of the metal slug having the surface as a bottom.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 15/226,170filed Aug. 2, 2016, which is based on and claims priority under 35 USC119 from Japanese Patent Application No. 2016-048865 filed Mar. 11,2016, the contents of all of which are incorporated herein by referencein their entireties.

BACKGROUND (i) Technical Field

The present invention relates to a method for producing a metalcylinder, a method for producing a substrate for an electrophotographicphotoreceptor, a method for manufacturing an electrophotographicphotoreceptor, and a metal slug for impact pressing.

(ii) Related Art

An apparatus which sequentially performs charging, exposure,development, transfer, cleaning, etc. by using an electrophotographicphotoreceptor (may be referred to as a “photoreceptor” hereinafter) hasbeen widely known as an electrophotographic image forming apparatus.

Known electrophotographic photoreceptors include afunction-separation-type photoreceptor in which a charge generationlayer that generates charge by exposure and a charge transport layerthat transports charge are laminated on a support having conductivitysuch as an aluminum support or the like, and a single-layer-typephotoreceptor in which the same layer performs both the function ofgenerating charge and the function of transporting charge.

For example, a method of adjusting the thickness, surface roughness, andthe like of an aluminum element tube by cutting the peripheral surfacethereof is known as a method for producing a cylindrical substrateserving as a conductive support of an electrophotographic photoreceptor.

On the other hand, impact pressing for forming a cylinder by applyingimpact with a punch to a metal slug placed in a die (female die) isknown as a method for mass-producing a thin metal container or the likeat low cost.

SUMMARY

According to an aspect of the invention, there is provided a method forproducing a metal cylinder including preparing a metal slug having asurface adjusted so that the crystal grain diameter at a depth of 10 μmfrom the surface is smaller than that at a depth of 100 μm from thesurface, and the crystal grain diameter at a depth of 10 μm from thesurface is 30 μm or more and 120 μm or less; and forming a cylinder byimpact pressing of the metal slug having the surface as a bottom.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIGS. 1A to 1C are schematic views showing an example of impact pressingin a method for producing a metal cylinder according to an exemplaryembodiment of the invention;

FIGS. 2A and 2B are schematic views showing an example of drawing andfine ironing in a method for producing a metal cylinder according to anexemplary embodiment of the invention;

FIG. 3 is a schematic partial sectional view showing an example of aconfiguration of an electrophotographic photoreceptor manufactured by amethod for manufacturing an electrophotographic photoreceptor accordingto an exemplary embodiment of the invention;

FIG. 4 is a schematic configuration diagram showing an example of animage forming apparatus according to an exemplary embodiment of theinvention;

FIG. 5 is a schematic configuration diagram showing another example ofan image forming apparatus according to an exemplary embodiment of theinvention; and

FIG. 6 is a schematic view showing a method for calculating a crystalgrain diameter.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention are described below withreference to the drawings. In the drawings, elements having the samefunction are denoted by the same reference numeral, and duplicatedescription is eliminated.

Method for Producing Metal Cylinder

A method for producing a metal cylinder according to an exemplaryembodiment of the invention includes preparing a metal slug having asurface adjusted so that the crystal grain diameter at a depth of 10 μmfrom the surface is smaller than that at a depth of 100 μm from thesurface, and the crystal grain diameter at a depth of 10 μm from thesurface is 30 μm or more and 120 μm or less; and forming a cylinder byimpact pressing of the metal slug having the surface as a bottom.

In general impact pressing, for example, a metal slug of aluminum or thelike (may be referred to as a “slug” hereinafter) is disposed in acircular female die, and a cylinder may be formed along a cylindricalmale die by striking with the die under high pressure.

For example, when a cylindrical substrate for an electrophotographicphotoreceptor is produced by impact pressing, the electrophotographicphotoreceptor is produced by molding a cylindrical aluminum tube byimpact pressing, then adjusting the inner and outer diameters,cylindricity, and circularity by ironing, and further forming aphotosensitive layer and the like on the outer peripheral surface of thecylinder.

However, when a cylinder is molded by impact pressing, many finerecesses may be produced at specific positions, and there is anindividual difference in the number of recesses. When a toner image isformed by an image forming apparatus provided with anelectrophotographic photoreceptor manufactured by forming aphotosensitive layer and the like on the outer peripheral surface ofsuch a cylinder having many recesses, an output image is influenced bythe recesses present on the outer peripheral surface of the cylinderdepending on the size of the recesses, and thus dot defects may occur inthe image.

When a cylinder is produced by impact pressing, the cause for theoccurrence of a recessed portion is unclear but is supposed as follows.

A phenomenon of so-called “surface roughness” which is caused by plasticdeformation of a metal occurs during impact pressing. The “surfaceroughness” represents projections and recesses formed in a surface of ametal, and it is considered that the projections among the projectionsand recesses of the surface are scraped by a female die to be flattened,while the recesses remain in the metal surface.

On the other hand, the method for producing a metal cylinder accordingto the exemplary embodiment of the invention may produce a metalcylinder with suppressed occurrence of recessed portions in the outerperipheral surface. The reason for this is considered as follow.

In impact pressing, the bottom of the slug before impact pressing ispartially extended to form the peripheral surface of the cylinder. The“surface roughness” described above is considered to occur due toprotrusion of crystal grains present at the bottom of the slug duringimpact pressing, and the larger the crystal grains, the higher thesurface roughness.

The method for producing a metal cylinder according to the exemplaryembodiment of the invention includes impact pressing the metal slughaving the surface (surface containing small crystal grains) as a bottomadjusted so that the crystal grain diameter at a depth of 10 μm from thesurface is smaller than that at a depth of 100 μm from the surface, andthe crystal grain diameter at a depth of 10 μm from the surface is 30 μmor more and 120 μm or less, thereby suppressing the occurrence ofsurface roughness. This is considered to be due to the fact that thecrystal grains become decreased in size by increasing the surfacehardness of the slug by shot peening, and accordingly the surfaceroughness is suppressed even during impact pressing, thereby suppressingthe occurrence of recesses in the outer peripheral surface of theresultant cylinder.

In addition, when the size of crystal grains in the slug surface isexcessively decreased by shot peening, the hardness is excessivelyincreased, and thus impact pressing becomes difficult.

The case of production of a cylindrical substrate for anelectrophotographic photoreceptor is specifically described as anexample of the method for producing a metal cylinder according to theexemplary embodiment of the invention.

For example, when a cylindrical substrate for an electrophotographicphotoreceptor is produced by the method for producing a metal cylinderaccording to the exemplary embodiment of the invention, a slug having asurface adjusted so that the crystal grain diameter at a depth of 10 μmfrom the surface is smaller than that at a depth of 100 μm from thesurface, and the crystal grain diameter at a depth of 10 μm from thesurface is 30 μm or more and 120 μm or less is prepared, the metal slugis molded into a cylinder by impact pressing of the metal slug with thesurface as a bottom, and the peripheral surface of the cylinder isironed. Each of the processes is described in detail below.

Preparation

In the preparation, the slug having a surface is prepared, the surfacebeing adjusted so that the crystal grain diameter at a depth of 10 μmfrom the surface is smaller than that at a depth of 100 μm from thesurface, and the crystal grain diameter at a depth of 10 μm from thesurface is 30 μm or more and 120 μm or less.

The material, shape, size, etc. of the slug may be selected according toapplication of the metal cylinder produced.

When the cylindrical substrate constituting an electrophotographicphotoreceptor is produced, an aluminum or aluminum alloy-made disk orcylindrical slug is used.

In addition, an elliptic cylindrical or prismatic slug, or the like maybe used according to application of the metal cylinder produced.

Examples of an aluminum alloy contained in the slug include aluminumalloys containing aluminum and, for example, Si, Fe, Cu, Mn, Mg, Cr, Zn,Ti, or the like.

The aluminum alloy contained in the slug used for producing thecylindrical substrate of the electrophotographic photoreceptor is aso-called 1000-series alloy.

From the viewpoint of workability, the aluminum content (aluminumpurity: weight ratio) in the slug is preferably 90.0% or more, morepreferably 93.0% or more, and further preferably 95.0% or more.

A method for forming the slug is not limited and, for example, when thecylindrical or disk-shaped slug is used, examples of the method includea method of cutting a rod-shaped metal material having a circularsection perpendicular to a longitudinal direction into a lengthcorresponding to the height (thickness) of the slug, a method ofpunching a circular shape in a metal plate having a thicknesscorresponding to the height (thickness) of the slug, and the like.

The slug has a columnar or disk-like shape and has a surface (endsurface) serving as a bottom (the surface opposite to the surface struckwith a male die and may be referred to as the “slug bottom” hereinafter)during impact pressing. In the exemplary embodiment, the slug preparedhas the surface serving as the bottom during impact pressing, in whichthe crystal grain diameter at a depth of 10 μm from the surface issmaller than that at a depth of 30 μm from the surface.

In the surface (slug bottom) serving as the bottom during impactpressing, the crystal grain diameter at a depth of 10 μm from thesurface is smaller than that at a depth of 100 μm from the surface, andthe crystal grain diameter at a depth of 10 μm from the surface is 30 μmor more and 120 μm or less. From the viewpoint of suppressing theoccurrence of recesses in the outer peripheral surface after impactpressing, the crystal grain diameter at a depth of 10 μm from thesurface of the slug bottom is preferably 40 μm or more and 100 μm orless and more preferably 40 μm or more and 70 μm or less.

Also, in the surface (slug bottom) of the slug serving as the bottomduring impact pressing, from the viewpoint of suppressing the occurrenceof recesses in the outer peripheral surface after impact pressing, thecrystal grain diameter at a depth of 100 μm from the surface ispreferably 50 μm or more and 160 μm or less, more preferably 70 μm ormore and 150 μm or less, and still more preferably 70 μm or more and 130μm or less.

In the exemplary embodiment, the crystal grain diameters at a depth of10 μm and a depth of 100 μm from the surface of the metal slug arevalues obtained by observation and measurement with a scanning electronmicroscope (SEM). Specifically, the crystal grain diameters are measuredas follows.

First, the metal slug is cut by using a cutting machine (Secotom-10,manufactured by Struers Inc.) in a direction perpendicular to thesurface serving as the bottom during impact pressing. Next, a cuttingsection is mirror-finished by polishing with a polishing machine (Beta &Vector GRINDER-POPLISHERS AND POWERHEAD, manufactured by Buhler Inc.) toform a sample. Then, the crystal grains in the section are observed witha scanning electron microscope (JSM-7500F, manufactured by JEOL Ltd.),and the crystal grain diameter is calculated.

In calculating the crystal grain diameter, as shown in FIG. 6, thesection in the observed image is photographed, and an assumed lineparallel to the surface (interface) is drawn at a position of 10 μm fromthe interface. The lengths of the crystals crossing the line(measurement length; 1000 μm) is number-averaged to determine thecrystal grain diameter.

A method for adjusting the slug bottom so that the crystal graindiameter at a depth of 10 μm from the surface is smaller than that at adepth of 100 μm from the surface, and the crystal grain diameter at adepth of 10 μm from the surface is 30 μm or more and 120 μm or less isnot particularly limited. The crystal grain range may be achieved by,for example, a method including shot-peening the bottom of the slugobtained by punching a metal plate or the like as described above. Theshot peening is a processing method for imparting work hardening andcompressive residual stress due to plastic deformation by projecting andcolliding steel-iron or non-ferrous metal particles on a surface to betreated.

In shot peening of the slug bottom, conditions may be determinedaccording to the material of the slug or the like so that the crystalgrain diameter at a depth of 10 μm from the surface is 30 μm or more and120 μm or less, and preferably the crystal grain diameter at a depth of100 μm from the surface is 50 μm or more and 160 μm or less.

The crystal grain diameter at the slug bottom during shot peening may becontrolled by the material, particle diameter, and shape of a projectionmaterial, projection pressure, projection time, projection distance (thedistance from the projection port of a shot peening apparatus to a plane(surface to be treated) of the slug), etc.

In the exemplary embodiment, examples of the projection material used inshot peening include zircon, glass, stainless, and the like.

The projection material preferably has a spherical shape or a shapeclose to the spherical shape, and the particle diameter of theprojection material is preferably 10 μm or more and 100 μm or less andmore preferably 10 μm or more and 50 μm or less from the viewpoint thatthe crystal grain diameter at a depth of 10 μm from the surface isadjusted to 30 μm or more and 120 μm or less, and preferably the crystalgrain diameter at a depth of 100 μm from the surface is adjusted to 50μm or more and 160 μm or less.

In addition, with increasing projection pressure, increasing projectiontime, or decreasing projection distance, the crystal grain diametertends to decrease, and each of the conditions may be selected accordingto the material of the slug, the intended crystal grain diameter, etc.

The apparatus for shot peening is not particularly limited and, forexample, the uniformity of the crystal grain diameter of the surface maybe improved by projecting the projection material on the slug bottomwhile rotating the slug using an apparatus provided with a mechanismwhich rotates a treatment body to be shot-peened.

The method for adjusting the slug bottom so that the crystal graindiameter at a depth of 10 μm from the surface is smaller than that at adepth of 100 μm from the surface, and the crystal grain diameter at adepth of 10 μm from the surface is 30 μm or more and 120 μm or less maybe a method without shot peening. For example, a usable method includesincreasing hardness by adding impurities to a material constituting theslug and adjusting the crystal grain diameter at a depth of 10 μm fromthe surface to 30 μm or more and 120 μm or less.

Impact Pressing

In the impact pressing, a cylinder is formed by impact pressing of theslug with the surface as the bottom.

FIGS. 1A to 1C show an example of molding of the cylinder by impactpressing of the slug.

A lubricant is applied to an end surface (slug bottom) of a cylindricalslug 30, and the slug 30 is placed in a circular hole 24 provided in adie (female die) 20 as shown in FIG. 1A. In this case, the slug 30 isplaced in the die 20 so that the end surface having a crystal graindiameter of 30 μm or more and 120 μm or less at a depth of 10 μm fromthe surface is located as the bottom.

Next, as shown in FIG. 1B, the slug 30 placed in the die 20 is pressedby a punch (male die) 21. Consequently, the slug 30 is extendedcylindrically from the circular hole of the die 20 so as to cover theperiphery of the punch 21. In this case, the bottom of the slug 30before impact pressing is partially extended to form the outerperipheral surface of a cylinder 4A, and thus the crystal grain diameterof the bottom of the slug 30 is reflected in the surface roughness ofthe outer peripheral surface of the cylinder 4A.

After molding, as shown in FIG. 1C, the punch 21 is removed by beingpulled up and passed through a central hole 23 of a stripper 22, therebyproducing the cylindrical compact (cylinder) 4A.

The impact pressing suppresses the occurrence of recessed portions inthe outer peripheral surface. In addition, hardness is increased by workhardening, and thus the cylindrical compact (cylinder) 4A having a smallthickness and high hardness may be produced.

The thickness of the cylinder 4A is not particularly limited but, forexample, when the cylinder 4A is produced as a cylindrical substrate foran electrophotographic photoreceptor, the thickness of the cylinder 4Amolded by impact pressing is preferably 0.4 mm or more and 0.8 mm orless and more preferably 0.4 mm or more and 0.6 mm or less from theviewpoint of processing to a thickness of, for example, 0.2 mm or moreand 0.9 mm or less by subsequent ironing while maintaining hardness.

Ironing

In the ironing, the inner and outer diameters, cylindricity,circularity, etc. are adjusted by ironing the cylinder molded by impactpressing.

When the cylindrical substrate for an electrophotographic photoreceptoris produced by using the method for producing a metal cylinder accordingto the exemplary embodiment, the ironing is performed. However, theironing may be performed according to demand in view of the purpose ofthe metal cylinder produced.

Specifically, as shown in FIG. 2A, if required, the cylinder 4A moldedby impact pressing is pushed from the inner side into a die 32 using acylindrical punch 31 to decrease the diameter by drawing. Then, as shownin FIG. 2B, the cylinder 4A is pushed into a die 33 having a smallerdiameter to perform ironing. The ironing may be performed withoutdrawing, or the ironing may be divided in plural steps. The thickness ofa cylinder 4B is adjusted by the number of times of ironing.

Also, stress may be released by annealing before ironing.

The thickness of the cylinder 4B after ironing is preferably 0.2 mm ormore and 0.9 mm or less and more preferably 0.4 mm or more and 0.6 mm orless from the viewpoint of maintaining the hardness as a substrate foran electrophotographic photoreceptor.

Therefore, when ironing is performed after the cylinder 4A is molded byimpact pressing according to the exemplary embodiment, the cylindricalsubstrate having little recessed portions in the outer peripheralsurface, a thin thickness, light weight, and high hardness may beproduced.

The method for producing a metal cylinder according to the exemplaryembodiment suppresses the occurrence of recessed portions in the outerperipheral surface and thus may produce a cylindrical substrate ofquality equivalent to or higher than a substrate produced by a cuttingmethod. Also, in mass production of metal cylinders, an automaticsurface test may be eliminated.

When the photoreceptor is used for a laser printer, the oscillationwavelength of a laser is preferably 350 nm or more and 850 nm or less,and the shorter the wavelength is, the more excellent resolution is. Thesurface of the cylindrical substrate is roughened to a surface roughnessRa of 0.04 μm or more and 0.5 μm or less in order to prevent theoccurrence of interference fringes during laser beam irradiation. With aRa of 0.04 μm or more, an interference preventing effect is obtained,while with a Ra of 0.5 μm or less, the tendency toward rough imagequality is effectively suppressed.

In addition, when incoherent light is used as a light source, rougheningfor preventing interference fringes is not particularly required, andthe occurrence of defects due to irregularity in the surface of thecylindrical substrate may be prevented, thereby causing suitability forlonger lifetime.

Examples of a roughening method include wet horning treatment ofspraying a suspension of an abrasive in water to the cylindricalsubstrate, center-less grinding treatment of continuously grinding thecylindrical substrate in pressure-contact with a rotating grindstone,anodization treatment, a method of forming a layer containing organic orinorganic semiconductor particles, and the like.

The anodization treatment includes forming an oxide film on an aluminumsurface by anodization using aluminum as an anode in an electrolytesolution. Examples of the electrolyte solution include a sulfuric acidsolution, an oxalic acid solution, and the like. However, a porousanodized film as it is after the treatment is chemically active and iseasily contaminated and has a large variation in resistance withenvironment. Therefore, sealing treatment is performed by treating theanodized film with steam under pressure or boiling water (to which ametal salt of nickel or the like may be added) to seal micro-pores byhydration reaction volume expansion and to convert the oxide to morestable hydrous oxide.

The thickness of the anodized film is preferably 0.3 μm or more and 15μm or less. With the thickness within the range, there is the tendencyto exhibit a barrier property against injection, and also there is thetendency to suppress an increase in remaining potential by repeated use.

The outer peripheral surface of the cylindrical substrate may be treatedwith an acid treatment solution or boehmite.

The treatment with an acid treatment solution is performed by using anacid treatment solution containing phosphoric acid, chromic acid, andhydrofluoric acid as described below. With respect to the ratios ofphosphoric acid, chromic acid, and hydrofluoric acid mixed in the acidtreatment solution, the ratio of phosphoric acid is within a range of10% by weight or more and 11% by weight or less, the ratio of chromicacid is within a range of 3% by weight or more and 5% by weight or less,the ratio of hydrofluoric acid is within a range of 0.5% by weight ormore and 2% by weight or less, and the total concentration of the acidsis preferably 13.5% by weight or more and 18% by weight or less. Thetreatment temperature is 42° C. or more and 48° C. or less, but a thickfilm may be more rapidly formed by maintaining the treatment temperaturehigh. The thickness of the film is preferably 0.3 μm or more and 15 μmor less.

The boehmite treatment is performed by immersing the cylindricalsubstrate in pure water at 90° C. or more 100° C. or less for 5 minutesor more and 60 minutes or less or by bringing the cylindrical substratein contact with heated steam at 90° C. or more 120° C. or less for 5minutes or more and 60 minutes or less. The thickness of the film ispreferably 0.1 μm or more and 5 μm or less. The film may furtheranodized by using an electrolyte solution with low film solubility, suchas a solution of adipic acid, boric acid, borate, phosphate, phthalate,maleate, benzoate, tartrate, citrate, or the like.

Method for Manufacturing Electrophotographic Photoreceptor

A method for manufacturing an electrophotographic photoreceptoraccording to an exemplary embodiment includes preparing, as a substratefor an electrophotographic photoreceptor, a metal cylinder produced bythe method for producing a metal cylinder according to the exemplaryembodiment, and forming a photosensitive layer on the outer peripheralsurface of the metal cylinder.

FIG. 3 is a schematic partial sectional view showing an example of alayer configuration of an electrophotographic photoreceptor produced bythe method for manufacturing an electrophotographic photoreceptoraccording to the exemplary embodiment. An electrophotographicphotoreceptor 7A shown in FIG. 3 has a structure in which an undercoatlayer 1, a charge generation layer 2, and a charge transport layer 3 arelaminated in that order on a cylindrical substrate 4, and the chargegeneration layer 2 and the charge transport layer 3 constitute aphotosensitive layer 5.

The electrophotographic photoreceptor is not limited to the layerconfiguration shown in FIG. 3, and for example, a protecting layer maybe further formed as an outermost layer on the photosensitive layer. Inaddition, the undercoat layer 1 need not be necessarily provided, and asingle-layer photosensitive layer in which the functions of the chargegeneration layer 2 and the charge transport layer 3 are integrated maybe provided.

Image Forming Apparatus (and Process Cartridge)

An image forming apparatus according to an exemplary embodiment includesan electrophotographic photoreceptor, a charging unit that charges thesurface of the electrophotographic photoreceptor, an electrostaticlatent image forming unit that forms an electrostatic latent image onthe surface of the charged electrophotographic photoreceptor, adevelopment unit that develops, with a developer containing a toner, theelectrostatic latent image formed on the surface of theelectrophotographic photoreceptor to form a toner image, and a transferunit that transfers the toner image to a surface of a recording medium.An electrophotographic photoreceptor manufactured by the method formanufacturing an electrophotographic photoreceptor according to theexemplary embodiment is used as the electrophotographic photoreceptor.

Examples of an image forming apparatus applied to the image formingapparatus according to the exemplary embodiment include known imageforming apparatuses such as an apparatus provided with a fixing unitthat fixes a toner image transferred to a surface of a recording medium;a direct-transfer type apparatus in which a toner image formed on thesurface of an electrophotographic photoreceptor is directly transferredto a recording medium; an intermediate transfer type apparatus in whicha toner image formed on the surface of an electrophotographicphotoreceptor is first transferred to a surface of an intermediatetransfer body and then the toner image transferred to the surface of theintermediate transfer body is second transferred to a surface of arecording medium; an apparatus provided with a cleaning unit that cleansthe surface of an electrophotographic photoreceptor before chargingafter transfer of a toner image; an apparatus provided with a staticeliminating unit that eliminates electricity in the surface of anelectrophotographic photoreceptor by irradiation with static eliminatinglight before charging after transfer of a toner image; an apparatusprovided with an electrophotographic photoreceptor heating member thatincreases the temperature of the electrophotographic photoreceptor todecrease the relative temperature; and the like.

In the case of the intermediate transfer-type apparatus, an example of aconfiguration applied to the transfer unit includes an intermediatetransfer body in which a toner image is transferred to a surface, afirst transfer unit in which the toner image formed on the surface ofthe electrophotographic photoreceptor is first transferred to thesurface of the intermediate transfer body, and a second transfer unit inwhich the toner image formed on the surface of the intermediate transferbody is second transferred to a surface of the recording medium.

In the image forming apparatus according to the exemplary embodiment,for example, a portion provided with the electrophotographicphotoreceptor may have a cartridge structure (process cartridge)detachable from the image forming apparatus. For example, a processcartridge used as the process cartridge is one provided with theelectrophotographic photoreceptor according to the exemplary embodiment.Besides the electrophotographic photoreceptor, the process cartridge maybe provided with at least one selected from the group consisting of acharging unit, an electrostatic latent image forming unit, a developmentunit, and a transfer unit.

An example of the image forming apparatus according to the exemplaryembodiment is described below, but the apparatus is not limited to thisexample. In addition, the portions shown in the drawings are described,and description of the other portions is omitted.

FIG. 4 is a schematic configuration diagram showing an example of theimage forming apparatus according to the exemplary embodiment.

As shown in FIG. 4, an image forming apparatus 100 according to theexemplary embodiment includes a process cartridge 300 provided with anelectrophotographic photoreceptor 7, an exposure device 9 (an example ofthe electrostatic latent image forming unit), a transfer device 40(first transfer device), and an intermediate transfer body 50. In theimage forming apparatus 100, the exposure device 9 is disposed at aposition where the electrophotographic photoreceptor 7 may be exposedfrom an opening of the process cartridge 300. The transfer device 40 isdisposed at a position facing the electrophotographic photoreceptor 7through the intermediate transfer body 50, and the intermediate transferbody 50 is disposed so as to be in partial contact with theelectrophotographic photoreceptor 7. Although not shown in the drawing,the image forming apparatus 100 also includes a second transfer devicethat transfers the toner image transferred to the intermediate transferbody 50 to the recording medium (for example, paper). The intermediatetransfer body 50, the transfer device 40 (first transfer device), andthe second transfer device (not shown) correspond to an example of thetransfer unit.

The process cartridge 300 shown in FIG. 4 includes a housing in whichthe electrophotographic photoreceptor 7, the charging device 8 (anexample of the charging unit), the development device 11 (an example ofthe development unit), and a cleaning device 13 (an example of thecleaning unit) are integrally supported. The cleaning device 13 has acleaning blade (an example of a cleaning member) 131 which is disposedin contact with the surface of the electrophotographic photoreceptor 7.The cleaning member may be a conductive or insulating fibrous member,not the form of the cleaning blade 131, and the cleaning member may beused singly or used in combination with the cleaning blade 131.

FIG. 4 shows an example of the image forming apparatus in which afibrous member 132 (roll-shaped) that supplies a lubricant 14 to thesurface of the electrophotographic photoreceptor 7, and a fibrous member133 (flat-brush-shaped) that assists cleaning are provided. However,these members are disposed according to demand.

FIG. 5 is a schematic configuration diagram showing another example ofthe image forming apparatus according to the exemplary embodiment.

An image forming apparatus 120 shown in FIG. 5 is a tandem-systemmulticolor image forming apparatus provided with four process cartridges300. The image forming apparatus 120 is configured so that the fourprocess cartridges 300 are arranged in parallel on an intermediatetransfer body 50, and an electrophotographic photoreceptor is used forone color. The image forming apparatus 120 has the same configuration asthe image forming apparatus 100 except being of a tandem system.

In the description of the embodiments, description is mainly made of acase in which the cylindrical substrate for an electrophotographicphotoreceptor is produced by the method for producing a metal cylinderaccording to the exemplary embodiment, but the method for producing ametal cylinder according to the exemplary embodiment is not limited tothe method for producing a cylindrical substrate for anelectrophotographic photoreceptor. The method for producing a metalcylinder according to the exemplary embodiment may be applied to, forexample, production of a cylindrical substrate such as a chargingroller, a transfer roller, or the like in an image forming apparatus,and production of a cylinder of an apparatus other than an image formingapparatus, such as a capacitor case, a battery case, a marker pen, orthe like.

EXAMPLES

Examples of the present invention are described below, but the presentinvention is not limited to these examples below.

Formation of Cylindrical Tube Comparative Example 1

An aluminum cylindrical slug having a diameter of 34 mm and a thicknessof 15 mm is prepared by punching an aluminum plate (A1070) having athickness of 15 mm. As a result of measurement of the crystal graindiameters at a depth of 10 μm and at a depth of 100 μm from the slugsurface by a known method, the crystal grain diameter at a depth of 10μm from the surface is 134. 2 μm, and the crystal grain diameter at adepth of 100 μm from the surface is 148.3 μm.

Then, a lubricant is applied to the surface of the slug, and the slug ismolded in a cylindrical shape having a diameter 34 mm by impactpressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, a recessed portion distribution on the outer peripheral surface ofthe resultant cylindrical tube is formed by using an automatic surfacetester, and the number of recessed portions (a diameter of 30 μm ormore) is measured.

Further, the positions of recessed portions in the outer peripheralsurface of the cylindrical tube are specified based on the recessedportion distribution, and the sizes (diameter) of the recessed portionsare measured by a laser microscope. As a result, the maximum size of therecessed portions is about 300 μm.

Example 1

An aluminum cylindrical slug having a diameter of 34 mm and a thicknessof 15 mm is prepared by punching an aluminum plate (A1070) having athickness of 15 mm.

The slug is shot-peened by using a shot peening apparatus (manufacturedby Fuji Manufacturing Co., Ltd.) under conditions below.

Projection material: manufactured by Fuji Manufacturing Co., Ltd.,zircon #400 (center particle diameter 45 μm)

Projection pressure: 0.25 MPa

Projection time: 10 seconds

Shot distance: 150 mm

Number of slug rotations: 40 rpm

As a result of measurement of the crystal grain diameters at a depth of10 μm and at a depth of 100 μm from the slug surface serving as thebottom in impact pressing by a known method, the crystal grain diameterat a depth of 10 μm from the surface is 44.7 μm, and the crystal graindiameter at a depth of 100 μm from the surface is 74.2 μm.

Then, a lubricant is applied to the shot-peened slug, and the slug ismolded in a cylindrical shape having a diameter 34 mm by impactpressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, the number and sizes of recessed portions (a diameter of 30 μm ormore) in the outer peripheral surface of the resultant cylindrical tubeare measured by the same method as in Comparative Example 1. As aresult, the number of recessed portions is decreased by about 80% ascompared with the cylindrical tube produced in Comparative Example 1,and the maximum size of the recessed portions is about 140 μm.

Example 2

A slug is prepared by the same method as in Example 1 and thensurface-treated by the same method as in Example 1 except that theprojection pressure of shot peening is changed to 0.15 MPa. As a resultof measurement of the crystal grain diameters at a depth of 10 μm and ata depth of 100 μm from the slug surface serving as the bottom in impactpressing by a known method, values shown in Table 1 below are obtained.

Then, a lubricant is applied to the shot-peened slug, and the slug ismolded in a cylindrical shape having a diameter 34 mm by impactpressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, the number and sizes of recessed portions (a dimeter of 30 μm ormore) in the outer peripheral surface of the resultant cylindrical tubeare measured by the same method as in Comparative Example 1. As aresult, the number of recessed portions is decreased by about 70% ascompared with the cylindrical tube produced in Comparative Example 1,and the maximum size of the recessed portions is about 150 μm.

Example 3

A slug is prepared by the same method as in Example 1 and thensurface-treated by the same method as in Example 1 except that theprojection pressure of shot peening is changed to 0.08 MPa. As a resultof measurement of the crystal grain diameters at a depth of 10 μm and ata depth of 100 μm from the slug surface serving as the bottom in impactpressing by a known method, values shown in Table 1 below are obtained.

Then, a lubricant is applied to the shot-peened slug, and the slug ismolded in a cylindrical shape having a diameter 34 mm by impactpressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, the number and sizes of recessed portions (a dimeter of 30 μm ormore) in the outer peripheral surface of the resultant cylindrical tubeare measured by the same method as in Comparative Example 1. As aresult, the number of recessed portions is decreased by about 60% ascompared with the cylindrical tube produced in Comparative Example 1,and the maximum size of the recessed portions is about 180 μm.

Example 4

An aluminum cylindrical slug having a diameter of 34 mm and a thicknessof 15 mm is prepared by punching an aluminum plate (A3003) having athickness of 15 mm. As a result of measurement of the crystal graindiameters at a depth of 10 μm and at a depth of 100 μm from the slugsurface serving as the bottom in impact pressing by a known method,values shown in Table 1 below are obtained.

Then, a lubricant is applied to the slug, and the slug is molded in acylindrical shape having a diameter 34 mm by impact pressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, the number and sizes of recessed portions (a dimeter of 30 μm ormore) in the outer peripheral surface of the resultant cylindrical tubeare measured by the same method as in Comparative Example 1. As aresult, the number of recessed portions is decreased by about 40% ascompared with the cylindrical tube produced in Comparative Example 1,and the maximum size of the recessed portions is about 180 μm.

Comparative Example 2

A slug is prepared by the same method as in Example 1 and thensurface-treated by the same method as in Example 1 except that theprojection pressure of shot peening is changed to 0.05 MPa. As a resultof measurement of the crystal grain diameters at a depth of 10 μm and ata depth of 100 μm from the slug surface serving as the bottom in impactpressing by a known method, values shown in Table 1 below are obtained.

Then, a lubricant is applied to the shot-peened slug, and the slug ismolded in a cylindrical shape having a diameter 34 mm by impactpressing.

Next, an aluminum cylindrical tube having a diameter of 30 mm, a lengthof 251 mm, and a wall thickness of 0.5 mm is formed by one time ofironing.

Then, the number and sizes of recessed portions (a dimeter of 30 μm ormore) in the outer peripheral surface of the resultant cylindrical tubeare measured by the same method as in Comparative Example 1. As aresult, the number of recessed portions is decreased by about 50% ascompared with the cylindrical tube produced in Comparative Example 1,and the maximum size of the recessed portions is about 250 μm.

Comparative Example 3

A slug is prepared by the same method as in Example 1 and thensurface-treated by the same method as in Example 1 except that theprojection pressure of shot peening is changed to 0.5 MPa. As a resultof measurement of the crystal grain diameters at a depth of 10 μm and ata depth of 100 μm from the slug surface serving as the bottom in impactpressing by a known method, values shown in Table 1 below are obtained.

Then, a lubricant is applied to the shot-peened slug, but the slugcannot be molded in a cylindrical shape by impact pressing. Theconceivable reason for this is that the slug hardness is excessivelyincreased by shot peening.

Evaluation of Cylindrical Tube

A recessed portion distribution on the outer peripheral surface of eachof the resultant cylindrical tubes is formed by using an automaticsurface tester, and the number of recessed portions (a dimeter of 30 μmor more) is measured. Further, the positions of recessed portions in theouter peripheral surface of the cylindrical tube are specified based onthe recessed portion distribution, and the sizes (diameter) of therecessed portions are measured by a laser microscope and evaluated basedon criteria below.

The slug of Comparative Example 3 cannot be molded into a cylinder, andthus a cylindrical tube cannot be evaluated.

Therefore, overall evaluation is “D” regardless of the criterial below.

The evaluation results are shown in Table 1. (Reduction rate of recessedportion)

A: A reduction rate of 50% or more as compared with Comparative Example1

B: A reduction rate of 25% or more and less than 50% as compared withComparative Example 1

C: A reduction rate of less than 25% as compared with ComparativeExample 1

Maximum Size of Recessed Portion

A: 150 μm or less

B: Over 150 μm and 200 μm or less

C: Over 200 μm

Overall Determination

A: Determination as “A” in evaluation of both the reduction rate ofrecessed portions and the maximum size of recessed portions

B: Determination as “A” in evaluation of one of the reduction rate ofrecessed portions and the maximum size of recessed portions anddetermination as “B” in evaluation of the other

C: Determination as “B” in evaluation of both the reduction rate ofrecessed portions and the maximum size of recessed portions

D: Determination as “D” in evaluation of at least one of the reductionrate of recessed portions and the maximum size of recessed portions

TABLE 1 Crystal grain Shot peening dimeter (μm) Evaluation of recessProjection Treatment Depth from Depth from Maximum size Reduction ratepressure time surface 10 surface 100 of recess of recess Overall (MPa)(sec) μm μm [μm] Determination [%] Determination determination Example 10.25 10 44.7 74.2 140 A 80 A A Example 2 0.15 10 67.1 122.5 150 A 70 A AExample 3 0.08 10 92.2 148.3 180 B 60 A B Example 4 Untreated (hardness109.5 134.2 180 B 40 B C increase by impurity) Comparative Untreated134.2 148.3 300 C — C D Example 1 Comparative 0.05 10 130.4 154.9 250 C50 A D Example 2 Comparative 0.5 10 26.5 154.9 Impossible to form intocylindrical tube D Example 3

Production of Electrophotographic Photoreceptor Formation of Substratefor Electrophotographic Photoreceptor

The aluminum cylindrical tubes produced in Examples 1, 2, 3, and 4 andComparative Examples 1 and 2 are used as conductive supports (substratesfor an electrophotographic photoreceptor) E1, E, E3, E4, C1, and C2,respectively.

Formation of Undercoat Layer

First, 100 parts by weight of zinc oxide (average particle diameter: 70nm, manufactured by Tayca Corporation, specific surface area value 15m²/g) is mixed with 500 parts by weight of tetrahydrofuran by stirring,and 1.3 parts by weight of a silane coupling agent (KBM503, manufacturedby Shin-Etsu Chemical Co., Ltd.) is added to the resultant mixture andstirred for 2 hours. Then, tetrahydrofuran is distilled off bydistillation under reduced pressure, and the residue is baked at 120° C.for 3 hours to produce zinc oxide surface-treated with the silanecoupling agent.

Then, 110 parts by weight of the surface-treated zinc oxide and 500parts by weight of tetrahydrofuran are mixed by stirring, and a solutionprepared by dissolving 0.6 parts by weight of alizarin in 50 parts byweight of tetrahydrofuran is added to the resultant mixture and stirredat 50° C. for 5 hours. Then, alizarin-added zinc oxide is filtered offby reduced-pressure filtration and then dried at 60° C. under reducedpressure to produce alizarin-added zinc oxide.

Then, 60 parts by weight of the alizarin-added zinc oxide, 13.5 parts byweight of a curing agent (blocked isocyanate Sumidur 3175, manufacturedby Sumitomo Bayer Urethane Co., Ltd.), 15 parts by weight of butyralresin (S-LEC BM-1, manufactured by Sekisui Chemical Co., Ltd.), and 85parts by weight of methyl ethyl ketone are mixed to prepare a mixedsolution. Then, 38 parts by weight of the mixed solution and 25 parts byweight of methyl ethyl ketone are mixed and dispersed for 2 hours with asand mill using glass beads of 1 mmφ to produce a dispersion.

To the resultant dispersion, 0.005 parts by weight of dioctyltindilaurate and 45 parts by weight of silicone resin particles (Tospearl145, manufactured by Momentive Performance Materials Inc.) are added,thereby producing a coating solution for forming an undercoat layer.

The resultant coating solution for forming an undercoat layer isapplied, by a dip coating method, to the outer peripheral surface ofeach of the cylindrical tubes E1, E2, E3, E4, C1, and C2 produced asconductive supports in the examples and comparative examples, and driedand cured at 170° C. for 30 minutes to form an undercoat layer having athickness of about 23 μm.

Formation of Charge Generation Layer

Next, 1 part by weight of hydroxygallium phthalocyanine having strongdiffraction peaks at Bragg angles (2θ±0.2°) of 7.5°, 9.9°, 12.5°, 16.3°,18.6°, 25.1°, and 28.3° in an X-ray diffraction spectrum is mixed with 1part by weight of polyvinyl butyral (S-LEC BM-S, manufactured by SekisuiChemical Co., Ltd.) and 80 parts by weight of n-butyl acetate, and theresultant mixture is dispersed together with glass beads in a paintshaker for 1 hour to prepare a coating solution for forming a chargegeneration layer. The resultant coating solution is applied, by a dipcoating method, to the conductive support on which the undercoat layerhas been formed, and dried by heating at 100° C. for 10 minutes to forma charge generation layer having a thickness of about 0.15 μm.

Formation of Charge Transport Layer

Next, 2.6 parts by weight of benzidine represented by formula (CT-1)below and 3 parts by weight of a polymer compound having a repeat unitrepresented by formula (B-1) below (viscosity-average molecular weight:40,000) are dissolved in 25 parts by weight of tetrahydrofuran toprepare a coating solution for forming a charge transport layer. Theresultant coating solution is applied, by a dip coating method, to thecharge generation layer and heated at 130° C. for 45 minutes to form acharge transport layer having a thickness of 20 μm. Consequently, eachof electrophotographic photoreceptors E1, E2, E3, E4, C1, is C2 areproduced.

Evaluation and Results

Each of the produced electrophotographic photoreceptors E1, E2, E3, E4,C1, and C2 is loaded on a process cartridge of DocuPrint P450manufactured by Fuji Xerox Co., Ltd., and a solid image (100% density)is output on A4 paper (manufactured by Fuji Xerox Co., Ltd., C2 paper)in an environment at 22° C. and 50% RH. The occurrence of white dots isevaluated in an image on the 5th paper based on criteria below.

The evaluation results are shown in Table 2.

Evaluation of White Dots

i) With respect to white dots of 0.7 mm or more

A: No occurrence

C: Occurrence of one or more

ii) With respect to white dots of 0.5 mm or more and less than 0.7 mm

A: No occurrence

B: Occurrence of one

C: Occurrence of two or more

iii) With respect to white dots of 0.3 mm or more and less than 0.5 mm

A: No occurrence

B: Occurrence of one or more and five or less

C: Occurrence of six or more

Overall Determination

A: Determination as “A” in the three items in evaluation of white dots

B: Determination as “A” in two items and “B” in one item in evaluationof white dots

C: Determination as “A” in one item and “B” in two items in evaluationof white dots

D: Determination as “A” in at least one of the items in evaluation ofwhite dots

TABLE 2 Number of white dots occurring 0.5 mm or 0.3 mm or Substrate formore and more and electrophotographic 0.7 mm less than less than Overallphotoreceptor or more Determination 0.7 mm Determination 0.5 mmDetermination determination E1 0 A 0 A 0 A A E2 0 A 0 A 0 A A E3 0 A 0 A1 B B E4 0 A 1 B 3 B C C1 3 C 8 C 15 C D C2 1 C 3 C 7 C D

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A metal slug comprising: a surface, wherein themetal slug is configured for impact pressing, wherein the surface isadjusted so that a crystal grain diameter in a direction parallel to thesurface at a depth of 10 pm from the surface is smaller than a crystalgrain diameter in the direction parallel to the surface at a depth of100 pm from the surface, and the crystal grain diameter at the depth of10 pm from the surface is 30 pm or more and 120 pm or less, wherein themetal slug comprises aluminum, wherein the metal slug is cylindrical,and wherein the metal slug has a diameter of 34 mm and a thickness of 15mm.
 2. The metal slug according to claim 1, wherein the crystal graindiameter at the depth of 100 μm from the surface is 50 μm or more and160 μm or less.
 3. The metal slug according to claim 1, wherein amaximum size of recessed portions in the surface is about 140 μm.
 4. Themetal slug according to claim 1, wherein a maximum size of recessedportions in the surface is about 150 μm.
 5. The metal slug according toclaim 1, wherein a maximum size of recessed portions in the surface isabout 180 μm.